Germany will deliver the first of four advanced IRIS-T air defence systems to Ukraine in the coming days to help ward off drone attacks, its defence minister Christine Lambrecht said during an unannounced visit to Odessa on Saturday.

As air raid sirens sounded in the port city above, Lambrecht held talks with her Ukrainian counterpart Oleksii Reznikov in an underground bunker. Lambrecht had extended a visit to nearby Moldova for the meeting.

"In a few days, we will deliver the very modern IRIS-T air defence system," she told ARD television. "It is very important for drone defence in particular."

Ukraine has been seeing more attacks from Iranian-made kamikaze drones in recent weeks, costing lives and causing serious damage to infrastructure.

It first emerged in May that Berlin was considering sending the IRIS-T surface-to-air defence system, which costs 150 million euros ($147 million) apiece.

The German armed forces themselves do not currently own the system, reckoned among the world's most advanced.

Earlier, meeting her Moldovan counterpart Anatolie Nosatii in Chisinau, she urged Western countries not to be deterred from arming Ukraine by threats that Russia could use nuclear weapons.

"We have to be very careful," she said. "But we mustn't let ourselves be paralysed."

Germany is facing calls to step up its support for Ukraine, including by sending offensive weapons such as the modern tanks Kyiv says it needs to take the fight to Russian forces.

Berlin has so far resisted such calls, arguing that such moves would escalate the situation and pointing out that no other country has so far sent tanks more modern than old Soviet stock sent by former Warsaw Pact countries.